Microwave devices for high power (mw/mmw) tubes are required to generate RF power outputs in the range of tens of Kilowatts to hundreds of Kilowatts as a function of frequency. These devices require cathodes capable of operating at current densities up to 12 A/cm.sup.2 in gridded devices. Present day state of the art cathodes operating at these current densities have a fairly short life. In high power (mw/mmw) tubes, in many cases, the life limiting component is the electron source.
The present state of the art for cathodes operating at current densities of 8 A/cm.sup.2 is to fabricate the matrix, and then impregnate the matrix with an impregnant that is some molar ratio of BaO, CaO and Al.sub.2 O.sub.3. Once the cathode is impregnated, the cathode is then given an overcoat of some platinum group metal. These cathodes give good life at current densities up to 8 A/cm.sup.2 operating in a pulse mode. Operating CW at 8 A/cm.sup.2, the relative life of these cathodes declines significantly. In addition to a deterioration in operating life when operated CW, the life of these cathodes can be adversely affected by back bombardment.